Recently, an illumination apparatus using white LEDs have been commercialized as a replacement for existing fluorescent lamps in a field of illumination. The LED illumination apparatuses have a merit that a life span thereof is longer than the fluorescent lamps. Also, because mercury is used in the fluorescent lamps, the LED illumination apparatuses are favored in terms of environmental burden.
In white LED illumination apparatuses, LED lamps are typically driven by a step-down chopper type DC/DC converter or a fly-back type DC/DC converter. For the LED lamps, a plurality of LED elements are connected in series to each other, thereby constantly keeping an electric current flowing through the LED elements, reducing a brightness variation between each LED element, and also ensuring a light intensity required for illumination.
Further, in a case of LED lamps requiring a higher light intensity, a plurality of rows of LED elements, which are connected in series to each other as described above, are connected in parallel to each other to form an LED group, thereby ensuring a higher light intensity.
However, although the LED illumination apparatuses have a long lifetime as described above, the LED illumination apparatuses have a finite life span of several ten thousand hours, and thus the LED lamps have to be replaced after all. In addition, because the LED lamps are configured by a plurality of LED elements connected in series to each other, if only one of the plurality of LED elements is disconnected/shorted, the LED lamps lose an illumination function, or the electric current flowing through the LED elements is increased, thereby shortening the life span.
To solve disconnection/short problems of the LED elements, JP-A-H06-291732 discloses an LED apparatus including a plurality of LED rows, each of which has a plurality of LED elements connected in series to each other and are connected in parallel to each other, and an electric current flowing through each LED group is detected by a detection resistor, so that a disconnection is detected based on decrease in voltage of the detection resistor.
Further, JP-A-2008-258428 discloses an LED illumination apparatus including an LED group having a plurality of LED rows connected in parallel to each other, in which a circuit open state is detected when an abnormality is occurred and thus any of LED rows are disconnected, so that an electric current of magnitude corresponding to LED rows having an abnormality is redistributed over LED rows other than the disconnected LED rows.